Global Warming Costs Starfish an Arm and a Leg

Stephan Reebs | September 29, 2008 09:40am ET

The oceans absorb about half the carbon dioxide humankind releases
into the atmosphere, and seawater is consequently acidifying.

That's a
big problem for shellfish, corals, and certain other calcareous creatures, because lowered pH dissolves their shells and skeletons. Echinoderms — starfish and their relatives — have calcium-based
skeletons, too, and so researchers have assumed they are likewise
subject to slow dissolution.

Hannah L. Wood of the Plymouth Marine Laboratory in England and two co-workers decided to check. They took brittlestars (Amphiura filiformis),
removed an arm or two, and then, to test how acidity affected
regeneration of the lost arms, exposed the animals to seawater that was
either normal (pH 8.0) or acidified (pH 7.7) — the standard worst-case prediction for the year 2100 — and pH 7.3).

To Wood's surprise, the brittlestars actually regenerated their arms
faster in the acidified seawater than in the normal stuff, showing that
they could lay down calcium effectively even under adverse conditions.

But there was a hidden cost. Both intact and regenerated arms
had considerably less muscle mass in acidified seawater than they did
in normal seawater. The low-pH animals consumed extra oxygen, so they
were working hard, and Wood thinks they had to burn muscle to fuel the
laborious regeneration. Weakened arms would undoubtedly affect feeding
and reproduction.

Thus, even if it doesn't affect their calcification, low pH still costs echinoderms an arm and a leg.